Realistic smell effect
Here is what I came up with (Since it wont be animated I decided not to use smoke sim).




I used grease pencil D+Mouse click to draw the smoke.
Convert stroke to curves then in the curve menu I had the fill set to HALF and extruded until it looked good.  
Then convert it to a mesh ALT+C.
I brought it into sculpt mode with a smooth brush and fixed all the wrinkles and odd looking things. Then used the blob brush to add thicker bulges where I thought they looked good. 
Duplicated the smoke and changed how it looked with more sculpting and scaling. 
The material added is just a simple diffuse (Principled BSDF) mixed with a transparent shader using a noise texture. I added a 2nd mix shader and transparent node to bring the overall transparency down. 


Hope this helps.